With increasing public awareness of the relatively high levels of air pollution which surround many parts of our nation, there has arisen a growing need for devices capable of cleaning the air. Such devices have a wide variety of applications, ranging from the smokestack where pollutants are produced to the homes of people living near sources of pollution. With regard to home applications, the need is particularly acute, inasmuch as many people are seriously affected by industrial pollutants as well as natural environmental particles such as pollen and the like.
One class of devices which is particularly effective in removing particles, such as pollen and soot, from the air generally includes an emitter which is driven by an extremely high voltage power supply. The emitter usually comprises a mesh of electrically-conductive material. When it is driven with a high voltage, the mesh emits a great quantity of charge which attaches itself to airborne particles thus giving them a charge.
The air to be cleaned is driven through the emitter by a fan or any other suitable apparatus. After being driven through the emitter and having its entrained particles given an electrical charge, the air is then blown into an electrostatic field between positively and negatively charged conducting filter elements. The voltage on the conducting filter elements is very high and, consequently, the entrained charged particles which are blown near them are attracted to and held by the charged filter element. They accumulate on the filter element which must be periodically washed.
Typical examples of such systems include those disclosed in U.S. Pat. Nos. 3,910,779, 2,129,783, 3,988,131, 2,885,026, 2,565,458, 3,950,153, and 3,594,989. While systems of this kind are extremely effective in removing particles from the air (they have efficiencies in the order of 98%), they have a number of distinct disadvantages. The voltages required for both the emitter and the filter itself are extremely high, typically in the order of 40-60 kilovolts. The use of such high voltages necessitates the use of relatively expensive equipment to generate these voltages. Thus, such air filters may be quite expensive. Still another problem is the fact that these filters must be cleaned frequently. This is a time consuming and clumsy operation.
Accordingly, a great deal of work has been expended in seeking alternatives to this type of filter. Perhaps the most common solution is simply to use a fiberglass or other mechanical air filter which is very inexpensive and hence can be disposed of. The use of a fiberglass filter also obviates the need for high voltage generating equipment. Such devices thus only have need of a blower and a filter and are relatively inexpensive. However, their efficiency is very low, typically in the order of about 2%.
Another approach is simply to eliminate the emitter. While the device does lose a good part of its efficiency, it has been noted that the presence of natural charges on air-borne particles is sufficient to cause the collection of about 85% of the particles when they are passed between a pair of oppositely charged conductive filter elements. However, the elimination of the emitter does little to reduce the cost of the device which still requires high voltage generating equipment. Again, the relatively expensive nature of the filter elements necessitates periodic cleaning.